Working with very large objects
There is no need to make it separate parts due to scale, but it is probably wise to break something like a spaceship into different parts (depending on the level of detail...more detail = more parts).

If your game engine is Unity (and most likely even if it isn't), you will want to use 1m = 1bu (blender unit) or switch to meters here:



As NoviceInDisguise mentioned in the comments, you may want to adjust the clipping distance in the 3D view if you are working with unusually large or small objects.